The reduction of high energy visible (HEV) light is useful in light filters because this reduction leads to reduced glare and increased eye protection. Also, the eye is much less sensitive to HEV (the violet and blue) light; so its reduction does not impact on the perception of adequate light intensity for normal vision. Melanin is a very useful pigment for the reduction of high energy visible light because it is able to reduce violet and blue without disturbing color perception. However, melanin occurs naturally in different colors (red, yellow, brown) and not all filter the HEV light in the same way.
U.S. Pat. No. 5,112,883 to James M. Gallas describes the broad use of melanin lenses in such light filters. More recently, in U.S. patent application Ser. No. 10/850,228 of Sugimura, Hideyo (published on Jan. 13, 2005), entitled “Photochromic Plate Containing Melanin,” melanin has been proposed to be used in combination with photochromic dyes because such a combination would provide a lightly-tinted HEV-absorbing lens (melanin alone) that would darken in light because of the presence of the photochromic dye (hereinafter referred to as the '228 application. However, the melanin described by the '228 application uses a brown melanin. While this brown melanin does reduce HEV light more than the non-HEV light at 550 nm—where the eye is most sensitive—the difference in the transmission is insignificant. That is, the brown melanin in the Sugimura patent will tend to also reduce a significant amount of green light as well as HEV light—unless the melanin concentration is low. However, if the melanin concentration is too low, then the use of melanin to reduce glare and offer protection from sunlight damage will have very little efficacy. This difficulty arises because the filtration is being shared by both melanin and a second dye (the photochromic dye). For this reason, Sugimura was forced to limit the concentration of melanin, and therefore its range of transmission. It ranged from 40% to 80%. This transmission range would preclude a very important application of the concept of a high energy visible (HEV) lens in combination with a photochromic dye in night driving lenses, which by European standards, cannot be lower than 80%.
The use of yellow melanin in accordance of the present invention as a filtering pigment offers several advantages over the prior art. These advantages will become evident in the following description.